I'm curious about your experience creating sleepyti.me. Care to write more about the subject?
I created http://sleepyti.me for a couple of reasons: first and foremost, I am not a morning person. I read with envy all of the HN posts about morning pages, getting up early with a cup of joe to be productive, etc. I am usually a groggy mess in the morning.
When I learned that you could time sleep cycles to reduce sleep intertia by waking up in between cycles, I immediately saw how it could help my life. Originally, I had written a shell script to help me personally (refre.sh to wake up refreshed), but it was difficult to distribute and my friends on a non-unix based OS couldn't use it at all.
I had recently been wanting to try my hand at developing web applications, and had decided to try jQuery. I am a security engineer and most of the code I write is for backend systems; basically, I'm not a design guy.
I learned jQuery and created sleepyti.me initially as a 'weekend project' (which, way back when, HN and reddit.com/r/web_design gave me feedback on) which I then expanded on until it was something I liked. I'm now in the final stages of developing an iPhone app (because of incessant demand via email) and soon Android, Windows Phone 7 and Blackberry versions.
The money comes in because of the traffic I've gotten. Someone (not me) submitted sleepyti.me to StumbleUpon very early in the site's lifecycle, and it has been quite popular there. I put a Facebook Like button on the page to try to drive the site socially/virally/"organically". This brought me between 10-15k hits a day -- a lot for a weekend project.
About two months after launch, someone (not me) submitted to Reddit's Today I Learned subreddit (regarding sleep inertia), which drove 250k+ hits in one day. After this event, my daily hits started averaging around 30k hits per day, which is where they are stable now.
Although obviously only a tiny amount of viewers click my banner ad, with an overall traffic amount this large there are bound to be people interested in whatever Adsense has spewing up. Additionally, I only show my banner ad after the calculation has occurred, so viewers don't have to suffer through ads. I've gotten emails from Google (automated of course) advising me to increase the banner count on the site, but I don't want to further bother viewers. If they're interested, they click; if not, no pressure.
My eventual goal would be to sell dedicated ad slots to an interested party (for example, a mattress chain that wants my visitors, or an alarm clock manufacturer, etc) or to sell the site at large to one of these entities. I'm not actively marketing it, however, and don't really even know how I'd go about it.
Not sure that you were looking for quite so in-depth of a reply, but I wanted to explain myself as I also saw another posting asking about the profit. Don't worry, I'm not a link spammer :)
Edit: As I seem unable to reply to the reply to this post, I will answer here. The 30k/day is from varied sources, as reddit traffic is generally short lived. I imagine that some of my 'dedicated audience' is from reddit, but a lot of it is users that found it shared on Facebook or located it via StumbleUpon.
The tutorials listed on their site are great to get something semi-functional, and I already knew HTML design so I could sort of throw things in tables to put them where I want them. I'm learning CSS3 now, so hopefully future projects will look a little prettier. I think this is one of the tutorials I used (if not, something similar): http://docs.jquery.com/Tutorials:Getting_Started_with_jQuery
The jQuery docs themselves provide in-depth examples and live demos, as well as well-written docs. The ones I found particularly useful were .get() for requesting PHP pages (although sleepyti.me doesn't use this) or loading dynamic data, .val() to check the value of an input and .html() (and append()) to append HTML to values in the document. fadeIn() and fadeOut() are nice for bringing pages into and out of view.
All in all, I was extremely impressed with how easy jQuery was to learn, and I'd recommend it to anyone with any kind of a development background looking to get into web design. If you have any questions, I've had excellent luck with simply searching stackoverflow.com. There's an answer for pretty much everything you could need on there :)